Voltage-dependent calcium channels (VDCCs) serve two critical functions: the regulation of cellular excitability, and the regulation of Ca2+ entry. Ca2+ dysfunction accompanies adult disease progression such as in cardiac hypertrophy. Thus, it follows that the chronic regulation of voltage-dependent Ca2+ channel expression is critical to the function of the heart and skeletal muscle. The guiding hypothesis of this proposal is that the Ras-related GTPase Rem regulates Ca2+ channel activity in cardiac and skeletal muscle by the novel mechanism of interacting with the beta-subunits of voltage-gated Ca2+ channels to block their association with alpha1-subunits. We hypothesize that this inhibits channel activity by blocking trafficking of functional calcium channels to the plasma membrane. This hypothesis was motivated by the following pilot studies: 1) Rem is highly expressed in cardiac and skeletal muscle. 2) Rem binds to beta- subunits. 3) Over-expression of wild-type Rem inhibits ionic current expression in heterologous expression systems, and importantly, in primary ventricular myocytes. 4) T-type Ca 2+ channels do not require accessory subunits and Rem does not inhibit expression of currents through this family of channels. This suggests that Rem regulates Ca2+ channel activity in a beta-subunit-dependent fashion. 5) Rem-mediated regulation of CaV1 channels is not understood, but initial studies have defined a crucial role for the Rem C-terminal domain in this process. We propose three specific aims to elucidate the function of Rem as a regulator of voltage-dependent Ca2+ channel activity. Specific Aim 1 will identify the amino acid sequences in Rem and the Ca2+ channel beta- subunit important for their interaction. Specific Aim 2 will determine if formation of the Rem:beta-subunit complex is regulated in vivo by 14-3-3 protein binding and GTPase activity. Studies will also examine the role of the C-terminal domain in Rem-mediated Ca2+ channel regulation. Specific Aim 3 will characterize the mechanism of Rem-mediated regulation of alpha1 channel activity by examining Rem effects on the association of alpha1 and beta-subunits and channel trafficking. These studies will advance knowledge by elucidating a new mechanism for controlling chronic Ca2+ channel activity as well as a novel mechanism for achieving cross talk between Ras-related GTPases and electrical signaling pathways. This knowledge could aid understanding of the regulation of voltage-dependent Ca2+ channels in both normal and disease states.